Thin film solid oxide fuel cells with nickel oxide–gadolinia doped ceria anodes deposited by sputtering were operated at 500 °C. The fuel cells each have 750 nm–yttria-stabilized zirconia electrolytes and 200 nm–platinum cathodes. The thicknesses of the anodes are 240 nm, 320 nm, and 400 nm. The cell with the 320-nm-thick anode showed the highest maximum power density among all cells. Through electrochemical impedance spectroscopy, the anodic activation resistance and the ohmic resistance were calculated. The anodic activation loss decreased with an increase in the anode thickness. Therefore, the cell with the 400-nm-thick anode showed the lowest activation polarization resistance. Additionally, the ohmic resistance, the sum of various electronic/ionic resistances, was lowest when using the 320-nm-thick anode. The electronic resistance and the ionic resistance of the anode were found to exist in a trade-off relationship owing to the current-collecting method of the anode.